In the field of focusing X-rays it is known to employ mirrors curved in one plane and flat in the orthogonal plane to produce focusing by reflection of the X-rays at glancing angles of incidence less than the critical angle of total external reflection. An example is shown in FIG. 1 of the accompanying drawings where M is the mirror, S the source and F the focus. These mirrors may have appropriate curvatures to produce convergent, divergent or parallel beams of X-rays. The curvatures may be produced by elastically bending plane plates or by appropriately grinding or otherwise shaping the mirror surface to the appropriate shape. It is also known to employ two such mirrors in tandem, each of which is curved in one plane only, the planes of curvature of the successive mirrors being perpendicular to one another so as to achieve the desired focusing in both planes by successive reflection at the two mirrors. In a known variant of this method two pairs of mirrors are used to produce a single point-focus, as shown in FIG. 2 of the accompanying drawing where M1 is a first pair of mirrors and M2 is the second pair of mirrors.
In most cases of interest the reflection only takes place at glancing angles of incidence below 1.degree.. The mirror surface must be extremely flat, surface irregularities being less than 1 nm in order to achieve a high reflectivity. The reflecting mirror surface usually consists of a dense metal such as gold or iridium deposited on a smooth mirror substrate. Alternatively, the substrate may be coated with many alternating layers of a dense and a less dense material to provide a multi-layer structure which acts as an artificial crystal and reflects X-rays within the wavelength range of interest for structural studies with a high efficiency.
The machining of mirror surfaces to achieve at the same time the desired shape and the necessary smoothness is a very expensive process. It is easier to polish flat surfaces of glass, silicon or other materials to the required smoothness but the means then used to bend the plates elastically to the correct shape occupy a considerable amount of space and often preclude the mirrors from being mounted close to one another or to the source of X-rays. Additional space is needed for the separate alignment adjustments required for each mirror. Typically these consist of at least one translational and one tilting adjustment per mirror. The invention aims to provide an improved way of supporting mirrors.